Offshore production platforms for oil and gas frequently have the need for pumps mounted on the platform. The pumps are used generally for transferring oil to gathering facilities and for injecting water into the wells. The most common type of pump used offshore is a positive displacement reciprocating pump.
While positive displacement pumps perform the job intended, large capacity positive displacement pumps are expensive, heavy and take up a large amount of space. Size and weight are particularly problems for offshore floating platforms. Minimizing space and weight on these platforms is very important.
Another type of pump commonly used in oilfield operations is an electrical submersible pump. These pumps are normally employed in a well for pumping fluid up the well to the surface. The pump is centrifugal, being made up of a large number of stages, each stage having an impeller and diffuser. The pump is driven by a downhole electric motor.
Electrical submersible pumps are also used on the surface for injecting water into wells for pressure maintenance and disposal. When used on the surface, the pumps are normally mounted horizontally with a thrust chamber and an electrical motor on one end. Additionally, these surface electrical centrifugal pumps have been mounted on a frame to incline them at an acute angle relative to horizontal.
A centrifugal electrical pump has certain advantages over positive displacement pumps for oilfield use. A centrifugal pump is normally less expensive in initial costs and it may have a lower maintenance cost. However, it is not uncommon for such a pump, even in a surface application, to be more than 30 feet in length. Because of the space required to support the pump horizontally, the length presents a disadvantage when employed offshore. Consequently, the use of centrifugal pumps as horizontally mounted surface pumps has been on land where is the length of the pump is not a disadvantage.